Communication apparatus

ABSTRACT

In a communication apparatus has a line control unit that controls connection with a communication line network, a communication unit transmits/receives data through the communication line network. A detection circuit detects one of a line voltage value and a line current value when the communication apparatus is connected to the line network. A memory unit stores multiple voltage-current characteristic curves defining relationships of line voltage values with respect to line current values satisfying a predetermined standard. An adjusting unit adjusts the line voltage value and the line current value so as to satisfy the predetermined standard based on one of the voltage-current characteristic curves stored in the memory unit. A selecting unit selects another voltage-current characteristic curve different from the one of the voltage-current characteristic curves from among the multiple voltage-current characteristic curves stored in the memory unit. A re-adjusting unit adjusts one of the line voltage and a line current.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from JapanesePatent Application No. 2005-003114, filed on Jan. 7, 2005. The entiresubject matter of the application is incorporated herein by reference.

BACKGROUND

1. Technical Field

Aspects of the present invention relate to a communication apparatus andin particular to a communication apparatus that controls to suppress anoscillation in a line communication network when the communicationapparatus is connected with a various kind of networks.

2. Description of Related Art

In order to maintain communication quality, a public line network isdesigned in accordance with predetermined standards. A communicationapparatus connected to such a network is configured such that a linevoltage or a line current is controlled so as to meet the standards,since a line resistance connected with an exchange installed in atelephone exchange station varies depending on the location of thecommunication apparatus.

For an example, Japanese Patent Provisional Publication P2004-112490Adescribes a communication apparatus that detects a line current and aline voltage, calculates line impedance, and adjusts the signal level ofthe modem based on the calculated impedance. Further, in order tocontrol the line current and the line voltage which meet the standardsof public line networks, etc., the apparatus adjusts a relation betweenthe current and the voltage so as to satisfy the standards, based on apredetermined DC mask curve defining a relationship between the linecurrent values and line voltage values. FIG. 10 is a graph showing anexample of the DC mask curve used in a conventional communicationapparatus.

In FIG. 10, a horizontal axis represents the line current value, while avertical axis represents the line voltage. An area between two dottedlines represents line current values and line voltage values satisfyingthe public line standards.

A predetermined DC mask curve passing the above area is defined(indicated by solid line in FIG. 10), and by controlling the impedanceof the line, the line current and the line voltage are adjusted.

For example, in FIG. 10, when initially a line current value and linevoltage value are represented by point A, which is out of the area,point A is located below the DC mask curve and the values do not meetthe standards. In such a case, the value of the line impedance ischanged to a smaller value. Then, the line current value and the linevoltage value are changed to values represented by point B. In thisexample shown in FIG. 10, point B is also out of the area (i.e., locatedabove the DC mask curve). Therefore, the value of the line impedance isthen changed to a larger value, and the line current value and the linevoltage value are changed to point C. As shown in FIG. 10, still point Cis out of the area (i.e., located below the DC mask curve), and thevalue of the line impedance is changed again to a smaller value. Then,the line current value and the line voltage value move to point D, whichis substantially on the DC mask curve. The line current value and theline voltage value set in this way satisfy the standards.

However, when the line current value and the line voltage value are setin the way described above, an oscillation may occur as the network isin the resonant state with specific frequencies. The oscillationfrequency is only within a frequency bandwidth from 20 kHz to 1 MHz,which is higher than an audio frequency range. However, the oscillationgenerated in the network would cause troubles such as generation ofnoises, malfunction in echo canceling while calling with a handset.

SUMMARY OF THE INVENTION

Aspects of the invention are advantageous in that there is provided animproved communication apparatus that can prevent an oscillation in acommunication line to which the apparatus is connected.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a perspective view of a communication apparatus according to afirst illustrative embodiment of the invention.

FIG. 2 is a block diagram showing an electronic configuration of thecommunication apparatus according to the first illustrative embodiment.

FIG. 3 is a block diagram showing a configuration of a line I/Faccording to the first illustrative embodiment.

FIG. 4 shows a table indicating DC mask curves stored in a ROM.

FIG. 5 shows a flowchart illustrating a DC mask curve selection processaccording to the first illustrative embodiment.

FIG. 6 shows a table of DC mask curves store in ROM according to asecond illustrative embodiment.

FIG. 7 shows a flowchart illustrating a DC mask curve selection processaccording to the second illustrative embodiment.

FIG. 8 shows a flowchart illustrating a DC mask curve selection processaccording to a third illustrative embodiment.

FIG. 9 shows a flowchart illustrating a DC mask curve selection processaccording to a fourth illustrative embodiment.

FIG. 10 is a graph showing a voltage-current characteristic and the DCmask curve according to the prior art.

FIG. 11 shows a flowchart illustrating the voltage-currentcharacteristic adjustment process according to the prior art.

DETAILED DESCRIPTION

General Overview

It is noted that various connections are set forth between elements inthe following description. It is noted that these connections in generaland unless specified otherwise, may be direct or indirect and that thisspecification is not intended to be limiting in this respect. Aspects ofthe invention may be implemented in computer software as programsstorable on computer-readable media including but not limited to RAMs,ROMs, flash memory, EEPROMs, CD-media, DVD-media, temporary storage,hard disk drives, floppy drives, permanent storage, and the like.

According to aspects of the invention, there is provided a communicationapparatus, which is provided with a line control unit configured tocontrol connection with a communication line network, a communicationunit configured to transmit and receive data through the communicationline network, a detection circuit configured to detect one of a linevoltage value and a line current value when the communication apparatusis connected to the line network, a memory unit configured to storemultiple voltage-current characteristic curves defining relationships ofline voltage values with respect to line current values, an adjustingunit configured to obtain the line voltage and the line current based onthe one of the line voltage value and the line current value, andadjusting the line voltage value and the line current value based on oneof the voltage-current characteristic curves stored in the memory unit,a selecting unit configured to select another voltage-currentcharacteristic curve which is different from the one of thevoltage-current characteristic curves from among the multiplevoltage-current characteristic curves stored in the memory unit, and are-adjusting unit configured to control the adjusting unit based on theselected voltage-current characteristic curve selected by the selectingunit.

The memory unit may store two voltage-current characteristic curves, andthe selecting unit may be configured to switch the selectedvoltage-current characteristic curve to the other voltage-currentcharacteristic curve when one of the line voltage and line current isadjusted by the adjusting unit.

The communication apparatus may further include an oscillation detectioncircuit that detects whether an oscillation is generated in thecommunication line network, and the selecting unit may select anothervoltage-current characteristic curve if the oscillation detectioncircuit detects that an oscillation is generated at the line voltage andthe line current adjusted by the adjusting unit.

The memory unit may store more than two voltage-current characteristiccurves, and the selecting unit may sequentially select one of thevoltage-current characteristic curve among more than two voltage-currentcharacteristic curves store in the memory unit if the oscillationdetection circuit detects the oscillation in the communication linenetwork after the line voltage and the line current are adjusted by theadjusting unit.

The communication apparatus may further include an oscillation detectioncircuit that detects whether an oscillation is generated in thecommunication line network, the oscillation detection circuit obtainingan oscillation frequency if the oscillation is detected. The memory unitmay store a voltage-current characteristic curve corresponding to theoscillation frequency if an oscillation is detected in the communicationline network, and the selecting unit may select the voltage-currentcharacteristic curve corresponding to the oscillation frequency detectedby the oscillation detection circuit from the ones stored in the memoryunit.

The memory unit may be configured to store multiple voltage-currentcharacteristic curves corresponding to an oscillation frequency of anoscillation generated in the communication line network, and anothervoltage-current characteristic curve corresponding to the oscillationfrequency detected by the oscillation detection circuit may be selectedif the oscillation detection circuit detects that an oscillation isgenerated in the communication line network at the line voltage valueand the line current value previously adjusted by the adjusting unit.

If the oscillation detection circuit detects an oscillation in thecommunication line network at the line voltage value and the linecurrent value adjusted with the adjusting unit, the selecting unitselects a different one of the multiple voltage-current characteristiccurves.

The selecting unit may includes a selected voltage-currentcharacteristic curve memory unit that stores the selectedvoltage-current characteristic curve, and the selecting unit may selecta voltage-current characteristic curve which is not store in the triedvoltage-current characteristic curve memory.

The communication apparatus may include an operable member that allows auser to manually select one of the multiple voltage-currentcharacteristic curves stored in the memory unit.

The operable member may allow a user to select one of the multiplevoltage-current characteristic curves when a connection with thecommunication line network is established.

According to aspects of the invention, there is also provided a methodof adjusting one of a line voltage and a line current applied to acommunication line of a communication apparatus. The communication lineis connected to a communication line network. The method includesstoring multiple voltage-current characteristic curves, adjusting one ofthe line voltage and the line current based one on of the multiplevoltage-current characteristic curves, detecting whether an oscillationis generated in a communication line network, transmitting and receivingdata through the communication line network, and re-adjusting one of theline voltage and the line current based on another one of the multiplevoltage-current characteristic curves.

According to aspects of the invention, there is further provided acomputer program product comprising computer readable instructions thatcause a computer to execute a method of adjusting one of a line voltageand a line current applied to a communication line of a communicationapparatus. The communication line is connected to a communication linenetwork. In this case, the method executed by the computer may includestoring multiple voltage-current characteristic curves, adjusting one ofthe line voltage and the line current based on one of the multiplevoltage-current characteristic curves, detecting whether an oscillationis generated in the communication line network, transmitting andreceiving data through the communication line network, and re-adjustingone of the line voltage and the line current based on another one of themultiple voltage-current characteristic curves.

ILLUSTRATIVE EMBODIMENTS

Hereinafter, referring to the accompanying drawings, communicationapparatuses according to illustrative embodiments of the invention willbe described.

FIG. 1 is a perspective view of a communication apparatus 1 according toaspects of a first embodiment of the invention. The communicationapparatus 1 is an MFP (Multi Function Peripheral) which has multiplefunctions such as functions of a facsimile machine, a copier, a scanner,a telephone, etc. The main unit 2 has an upper body portion 2 b and abottom portion 2 a. The upper body portion 2 b is attached to the bottomportion 2 a such that the upper body portion 2 b is moved betweenopen/closed positions with respect to the bottom portion 2 a. Further, aprinter 25 is built in the bottom portion 2 a as shown in FIG. 2.

An operation panel 4 is formed on the front side of the upper bodyportion 2 b. The operation panel 4 includes switches to control multiplefunctions of the facsimile machine, copier, scanner, etc., numeric keysto input numerals, a cursor key 4 a to move a cursor displayed on adisplay unit 5, a confirm key (enter key) 4 b which is to be pressed bya user for confirmation of input setting, and the display unit 5(hereinafter referred to as an “LCD”).

An original document outlet 7 and an original document insertion slot 8are formed in the upper body portion 2 b. Original documents insertedthrough the original document insertion slot 8 are transmitted to theoriginal document outlet 7 while the documents are read by a scanner(CIS: Contact Image Sensor) built in the upper body portion 2 b (notshown) and image data is generated.

In addition to the CIS built in the upper body portion 2 b, anotherscanner is built in the bottom portion 2 a, which reads originaldocuments placed on a platen glass extending horizontally beneath anoriginal document cover 6.

A recording paper tray (not shown) is placed on a lower side of thebottom portion 2 a. The image data generated by the CIS, generated bythe scanner 22 or received by the facsimile is printed by the printer 25on the recording paper transported from the record paper tray.

Referring now to FIG. 2, an electric configuration of the communicationapparatus 1 will be described. FIG. 2 is a block diagram showing theelectronic configuration of the communication apparatus 1. Thecommunication apparatus 1 includes a CPU 11, ROM 12, EEPROM 13, RAM 14,image memory 15, a line I/F section 19, a modem 20, a buffer 21, ascanner 22, an encoding section 23, a decoding section 24, a printer 25,an operation panel 4, an LCD 5 and an amplifier 27, which are connectedto each other through a bus line 30.

The line I/F section 19 is provided for performing line control, and hasa semiconductor DAA (Data Access Arrangement) 33 (see FIG. 3), Thecommunication apparatus 1 is connected, through the line I/F section 19,to a telephone line 31. The line I/F section 19 receives various signalssuch as a call signal and a signal indicating the telephone number of acalling station which are transmitted from an exchange 29. The line I/Fsection 19 also operate to transmit a dial signal at the calling timeresponsive to key operations through the operation panel 4 to theexchange 29. An external telephone 3 is connected via external telephoneterminals T1 and T2.

The CPU 11 controls the sections connected by the bus line 30 inaccordance with various signals transmitted and received through theline I/F section 19. The ROM 12 is a read only memory storing controlprograms executed by the CPU 11, and it includes DC mask curve memory 12a storing multiple DC mask curves which are used to control a linevoltage value and a line current value.

The RAM 14 is a rewritable memory for temporarily storing various piecesof data while the CPU 11 executes control programs. The RAM 14 alsoincludes a temporary memory 14 a storing identifier (temp) which isreferred to for identifying a type of the selected DC mask curve, andtried DC mask identifier memory 14 b storing the identifiers of thetried DC mask curves.

The EEPROM 13, which is an electrically erasable nonvolatile memory,includes a DC mask curve identifier memory 13 a and a DC mask curvesetting complete flag memory 13 b. The DC mask curve identifier memory13 a stores the identifier of the DC mask curve to be used to adjust thecommunication line among multiple DC mask curves stored in the ROM 12.The DC mask curve setting complete flag memory 13 b stores the flagwhich indicates whether the identifier of the DC mask curve is set ornot.

The image memory 15 is a memory for storing image data. The receivedimage data is once stored in the image memory 15 and after the imagedata is printed on the recording paper by the printer 25, the image datais deleted from the image memory 15. The image data generated by thescanner 22 is also stored in the image memory 15. When the facsimiletransmission function is set, the image data is sent via the line I/Fsection. When the copier function is set, the image data is printed onthe printer 15, and then deleted from the image memory 15 afterward.

The modem 20 modulates and demodulates image information andcommunication data for transmission and also transmits and receivesvarious procedure signals for transmission control. The buffer 21temporarily stores data containing encoded image information transmittedto and/or received from an opposite station.

The scanner 22 reads an original document inserted to an originalinsertion slot 8 or placed on a platen glass and generates image dataThe encoding section 23 encodes the image data generated by the scanner22. The decoding section 24 reads the image data stored in the buffer 21or the image memory 15 and decodes the image data. The decoded data isprinted on recording paper by the printer 25.

The printer 25 according to the illustrative embodiment is an ink jetprinter and prints images on the recording papers based on the imagedata. The amplifier 27 amplifies electronic signals of ringing tones andvoices, and drives a loudspeaker 28 to output sound (voice).

The communication apparatus I described above is connected to thetelephone line 31 through the line I/F section 19. The telephone line 31is connected to the exchange 29. The exchange 29 is connected to anotherexchange via a telephone line 32. The other exchange is furtherconnected to another machine at a calling station or at a destination.

FIG. 3 is a block diagram showing the configuration of the line I/Fsection 19. The line I/F section 19 includes the semiconductor DAA 33, aCML (Connect MODEM to Line) relay 36 for switching between the telephoneand the facsimile, a rectifier bridge 37, and DC loop cut capacitors 38a, 38 b, 38 c and 38 d, a transistor 45, and an oscillation detectioncircuit 50, etc. In FIG. 3, L1 and L2 are terminals to the telephoneline 31, and T1 and T2 are terminals to the external telephone 3.

The semiconductor DAA 33 and the modem 20 are insulated in terms of thedirect current. Both of them are connected to an insulation section 35transmitting data, signals, etc., and a transformer supplying electricpower to the semiconductor DAA 33.

The semiconductor DAA 33 is provided with a hybrid network 44, a CODEC40, a ring detection circuit 39, a transmission amplifier 42, a toneamplifier 43, a serial I/F 41 and a voltage detection circuit 34.

The hybrid network 44 establishes connection with the network anddisconnection therefrom. The hybrid network 44 includes a two-wire tofour-wire conversion circuit for converting facsimile data via thetelephone line 31 into transmission data and received data, a cancellercircuit for suppressing wraparound routing of transmission data to areception path, a filter circuit, and etc. The hybrid network 44 isconnected to the positive electrode of the rectifier bridge 37 through acondenser and a resistor. It is also connected to the CODEC 40 via atransmission amplifier 42, and to the base of the transistor 45, and tothe serial I/F 41.

The CODEC 40 performs A/D conversion and D/A conversion of facsimilereception data and transmission data. The CODEC 40 is connected to thecommunication line network and the external telephone 3 through the toneamplifier 43, and is also connected to the hybrid network 44 trough thetransmission amplifier 42.

The transmission amplifier 42 performs gain adjustment of transmissiondata. The tone amplifier 43 is a differential amplifier and receivesdifferential input from the terminals L1 and L2 of the telephone line31.

When the CODEC 40 receives a tone signal from the telephone line 31 orthe external telephone 3, the received tone signal is transmittedthrough the tone amplifier 43, the CODEC 40, the serial I/F 41, theinsulation section 35, and the modem 20 in this order. And the tonedetection signal transmitted from the CODEC 40 is transmitted to the CPU11.

The ring detection circuit 39 is connected to the communication linenetwork and the external telephone 3 through the loop cut capacitors 38a and 38 b. The output terminal of the ring detection circuit 39 isconnected to the serial I/F 41. When a ring signal reaches the ringdetection circuit 39, the ring detection circuit 39 detects the same andoutputs the ring detection signal to the serial I/F 41.

The serial I/F converts the ring detection signals input from the ringdetection circuit 39 and facsimile reception data input from the CODEC40 to serial signals, and transmits the serial signals to the modem 20through the capacitor 35 b. It also receives a control signal toestablish the connection to or disconnect from the communication linenetwork and facsimile transmission data from the modem 20 via thecapacitor 35 a, and separates them respectively. The voltage detectioncircuit 34 is connected to the rectifier bridge 37 via a resistor andobtains the line voltage value.

The transistor 45 adjusts the line voltage to fit the predeterminedvoltage current characteristic, based on the value obtained by thevoltage detection circuit 34. The line impedance can be adjusted bychanging the base voltage of the transistor 45.

The oscillation detection circuit 50 obtains the oscillation frequencywhen a connection with the network through the telephone line 31 isestablished and an oscillation occurs in the network. The oscillationdetection circuit 50 includes circuits which can detect the oscillationwithin a predetermined bandwidth. Specifically, the oscillationdetection circuit 50 applies the line voltage to band-path filterscorresponding to, for example, from 20 kHz to 100 kHz, from 100 kHz to200 kHz, from 200 kHz to 750 kHz, and 750 kHz to 1 MHz, and if the levelof the voltage output from a bandpass filter is higher than thepredetermined level, the oscillation detection circuit 50 determinesthat the oscillation occurs within the frequency range. Further, theoscillation detection circuit 50 is connected to the communication linenetwork through L1 and L2, and the oscillation detection signals aretransmitted to the CPU 11.

Next, processing of the voltage current characteristic adjustmentexecuted when the communication apparatus 1 configured as describedabove starts receiving or transmitting the information, will bediscussed with reference to a flowchart of FIG. 11. FIG. 11 is aflowchart showing how the voltage current characteristic adjustment isexecuted according to the predetermined DC mask curves stored in thecommunication apparatus 1. The process is executed after the connectionwith the network is established.

First, the line voltage value detected by the voltage detection circuit34 is checked (S71). Whether or not the line voltage value exceedsathreshold voltage (e.g., 100 V) is determined. If the line voltagevalue does not exceeds (No at S72), the line network is in normal state.Then, the line current value is acquired based on the currently set DCimpedance (S73). Next, It is determined whether or not the detected linevoltage value is within +/−0.5 V of the decided voltage which is on thecurrently set DC mask curve and corresponding to the acquired linecurrent value. Here, the currently set DC mask curve means thepre-determined DC mask curve to be applied for voltage-currentcharacteristic adjustment process. When multiple DC mask curves arestore in ROM 12, an identifier is stored in a DC mask curve identifiermemory 13 a of EEPROM 13. When trials are done to select an adequate DCmask curve, the identifier is stored in Temp memory 14 a of RAM 14.

If the line voltage is not within +/−0.5 V of the decided voltage valuebased on the DC mask curve (No at S74), the base voltage of thetransistor 45 is varied to adjust the line impedance (S75), then theprocess goes back to S71

If the line voltage is within +/−0.5 V of the decided voltage valuebased on the DC mask curve (Yes at S74), the voltage-currentcharacteristic adjustment process terminates. On the other hand, in theprocess of S72, if the line voltage value exceeds (Yes at S72), the linenetwork is in abnormal state. Then, the connection with thecommunication line network is cut off (S76), and the voltage-currentcharacteristic adjustment process terminates.

As described above, when transmitting and receiving begin, the linevoltage and the line current are adjusted based on the DC mask curvewhich is set to meet the required characteristic by the standards.

Next, the DC mask curve selection process will be discussed withreference to a table of DC mask curves shown in FIG. 4, and a flow chartshown in FIG. 5, iwhen the user installs the communication apparatus 1,namely, when the user turns on the power.

FIG. 4 is a table which shows the DC mask curves stored in the DC maskcurve memory 12 a of the ROM 12. The ROM 12 stores the DC mask curvescorresponding to 5 oscillation statuses of the communication network.Each DC mask curve represents 5 points of the voltage-currentcharacteristic. Those points are stored in the memory, the valuesbetween two neighboring points being calculated using linearinterpolation method.

The DC mask curve shown in the first row of the table corresponds to nooscillation, which has a identifier A. As described above, thevoltage-current characteristic is defined by the five points indicatedin the table. The first point has the voltage value of 4000 mV(4 V), andthe current value of 20 mA. The second point has the voltage value of 4V and the current value of 40 mA. The third point has the voltage valueof 8 V and the current value of 40 mA. The fourth point has the voltagevalue of 9.5 V and the current value of 60 mA. The fifth point has thevoltage value of 15 V and the current value of 150 mA.

For example, a point corresponding the current value 10 mA is not storedin the memory, the point is located between the first point (4 V, 0 mA)and the second point (4 V, 20 mA), therefore, the voltage value iscalculated to be 4 V. Similarly, if a current value is 30 mA, the pointis located between the second point and the third point. In this case,the voltage value is calculated to be 6 V.

In the second row of the table, the DC mask curve which is applied whenan oscillation is generated and its oscillation frequency ranges between20 kHz and 100 kHz, is shown. The curve is stored in the memory and hasan identifier B. The voltage value and the current value of the firstpoint are 5 V and 0 mA. The voltage value and the current value of thesecond point are 6 V and 21 mA. The voltage values and the currentvalues of the other points are as indicated in the table.

Similarly, in the third row of the table, the DC mask curve which isapplied when an oscillation is generated and its oscillation frequencyranges between 100 kHz and 200 kHz. The curve has an identifier C. Inthe fourth row, the DC mask curve is shown which is applied when anoscillation is generated and its oscillation frequency ranges between200 kHz and 750 kHz. It has an identifier B. In the fifth row, the DCmask curve is shown which is applied when an oscillatin is generated andits oscillation frequency ranges between 750 kHz and 1 MHz, and it hasan identifier D. As above, each row of the table shown in FIG. 4indicates 5 pairs of voltage values and current values defining a DCmask curve.

In this example show in FIG. 4, when the oscillation frequency rangesbetween 20 kHz and 100 kHz, and when the oscillation frequency rangesbetween 200 kHz and 750 kHz, the same DC mask curve (identifier: B) isused. Further, the DC mask curve (identifier: A) shown in the first rowis a default DC mask curve. If the DC mask curve is applied and theoscillation is not generated, this DC mask curve is set to be applied tothe communication apparatus 1.

Next, the DC mask curve setting process is discussed with reference tothe flowchart shown in FIG. 5. The DC mask curve setting process isexecuted when the communication apparatus 1 is powered on.

First, the line voltage value detected by the voltage detection circuit34 is checked (S1). Then, it is judges whether the line voltage value isequal to or greater than the minimum voltage which allows thecommunication apparatus 1 to connect with the communication line network(S2). If the line voltage is equal to or greater than the minimumvoltage (Yes at S2), the DC mask curve setting complete flag memory 13 bis checked, and it is judged whether a DC mask curve has already beenset (S3). If the DC mask curve has not been set (No at S3), theidentifier A is stored in the Temp memory 14 a (S4), and the line isdisconnected (S5). Next, the voltage-current characteristic adjustmentprocess (see FIG. 11) is executed (S6). In the voltage-currentcharacteristic adjustment process, the line voltage and line current areadjusted in accordance with the DC mask curve 1 having the identifier ofA that is stored in ROM 12.

Subsequently, after the adjustment is done in the voltage-currentcharacteristic adjustment process, it is judged whether the oscillationis generated in the communication line network based on the oscillationdetection signal output by the oscillation detection circuit 50 (S7). Ifthe oscillation is not generated (No at S7), an identifier is set to Aas the DC mask curve having identifier A is applied. Here, setting anidentifier of the DC mask curve as A, an identifier A is stored in theDC mask curve identifier memory 13 a of EEPROM 13. Thereafter, whentransmission/reception process begins, the voltage-currentcharacteristic adjustment process is executed based on the identifier ofthe DC mask curve set as above,

If it is determined that the oscillation is generated in thecommunication line network (Yes at S7), it is judged whether theoscillation frequency ranges between 20 kHz and 100 kHz, or between 200kHz and 750 kHz (S9). If the oscillation frequency ranges between 20 kHzand 100 kHz, or between 200 kHz and 750 kHz (Yes at S9), the identifierof the DC mask curve to be applied is set to B (S10).

If the oscillation frequency does not range between 20 kHz and 100 kHz,or between 200 kHz and 750 kHz (No at S9), it is judged whether theoscillation frequency ranges between 100 kHz and 200 kHz based on theoscillation detection signal output from the oscillation detectingcircuit 50 (S11). If the oscillation frequency ranges between 100 kHzand 200 kHz (Yes at S11), the identifier of the DC mask curve to beapplied is set to C (S12). If the oscillation frequency does not rangebetween 100 kHz and 200 kHz (No at S11), the identifier of the DC maskcurve to be applied is set to D (S13).

When the DC mask curve setting is completed in S8, S10 or S13, theconnection with the communication line network is released (i.e.,disconnected) (S14), a setting complete flag is set in the DC mask curvesetting flag memory (S15), and the DC mask curve setting processterminates. If the line voltage is not equal to or greater than theminimum voltage enabling connection with the communication line network(No at S2), or the DC mask curve has already been set (Yes at S3), theDC mask curve setting process terminates. After termination of thisprocess, the communication apparatus pauses until information isreceived or a user makes an operation, and a corresponding process isexecuted according to the received information or the operation the usermade. As described above, according to the communication apparatus 1according to the fist embodiment, the predetermined (default) DC maskcurve and some other DC mask curves which correspond to the oscillationfrequencies when the oscillation is generated and can be used to cancelthe oscillation. When the communication apparatus is installed firsttime, the predetermined (default) DC mask curve is applied to adjust thevoltage-current characteristic. If the oscillation is generated at thedetermined characteristic, the adequate DC mask curve is set accordingto the oscillation frequency. Therefore, the communication apparatus 1itself can suppress the oscillation in the communication line network.

Next, the second embodiment will be described with reference to FIGS. 6and 7. Here, description similar to that of the first embodiment of thecommunication apparatus 1 will be omitted for the brevity, anddescription is made only on the different portions. In the firstembodiment, the voltage-current characteristic is adjusted based on thepredetermined (default) DC mask curve, then after the adjustment isdone, if the oscillation occurs, another adequate DC mask curve isselected according to the oscillation frequency. In the secondembodiment, multiple DC mask curves are store corresponding to theoscillation frequency ranges. When the voltage-current characteristic isadjusted based on the selected DC mask curve corresponding to theoscillation frequency, but still an oscillation is generated at the samefrequency, then, another DC mask curve can, be selected corresponding tothe same oscillation frequency.

FIG. 6 shows a table of DC mask curves store in the DC mask curve memory12 a of ROM 12 according to the second embodiment. Similar to the firstembodiment, the DC mask curve memory 12 a stores DC mask curvescorresponding to 5 oscillation states. Three DC mask curves are storedcorresponding to each of the four kinds of oscillation frequencybandwidths.

Each DC mask curve is defined by 5 points of the voltage-currentcharacteristic, the values between two neighboring points are calculatedin accordance with the linear interpolation method as in the firstembodiment. The DC mask curve labeled as “NO OSCILLATION” (first row) isthe same curve which has identifier A in the first embodiment.

Three DC mask curves identified as B1, B2 and B3 corresponding to theoscillation frequency from 20 kHz to 100 kHz are defined on the secondto fourth rows of the table shown in FIG. 6. Three DC mask curvesidentified as C1, C2 and C3 corresponding to the oscillation frequencyfrom 100 kHz to 200 kHz are defined on the fifth to seventh rows of thetable. Three DC mask curves identified as D1, D2 and D3 corresponding tothe oscillation frequency from 200 kHz to 750 kHz are defined on theeighth to tenth rows of the table. Three DC mask curves identified asE1, E2 and E3 corresponding to the oscillation frequency from 750 kHz to1 MHz are defined on the eleventh to thirteenth rows of the table.

Next, the DC mask curve setting process according to the secondembodiment will be described with reference to the flowchart shown inFIG. 7. The process is executed when the communication apparatus 1 ispowered on.

First, the line voltage value detected by the voltage detection circuit34 is checked (S21). Then, it is judged whether the line voltage valueis equal to or greater than the minimum voltage which allows thecommunication apparatus 1 to connect with the communication line network(S22). If the line voltage is equal to or greater than the minimumvoltage (Yes at S22), the DC mask curve setting complete flag memory 13b of EEPROM 13 is checked, and it is judged whether the DC mask curvehas already been set (S23). If a DC mask curve has not been set (No atS23), the identifier A is stored in the Temp memory 14 a (S24), and theconnection with the network is cut (S25). Next, the voltage-currentcharacteristic adjustment process shown in FIG. 11 is executed (S26),and the line voltage and the line current are adjusted based on the DCmask curve identified by the identifier stored in the Temp memory 14 a.

Subsequently, after the adjustment is done in the voltage-currentcharacteristic adjustment process, it is judged whether the oscillationoccurs in the communication line network in accordance with theoscillation detection signal output by the oscillation detection circuit50 (S27). If the oscillation is generated in the communication linenetwork (Yes at S27), the oscillation frequency is acquired from theoscillation detection signal output by the oscillation detection circuit50, and it is judged whether an untried DC mask curve exists among DCmask curves corresponding to the oscillation frequency stored in ROM 12referring to the tried DC mask identifier memory 14 b of RAM 14 (S28).The ROM 12 stores multiple DC mask curves corresponding to respectiveoscillation frequency bandwidths, and identifiers of the already triedDC mask curves are stored in RAM 14 in S29, which is described later.

If one or more untried DC mask curve exists (Yes at S28), one of them isselected in the order stored in the table, and the identifier of theselected DC mask curve is stored in the tried DC mask identifier memory14 b (S30) as well as in The Temp memory 14 a, and the process returnsto S25. So, thereafter, the voltage-current characteristic adjustmentprocess S26 is executed based on the DC mask curve selected in S29.

If it is determined that an oscillation is not generated in the network(No at S27), the DC mask curve identifier stored in the Temp memory 14 ais set in the DC mask curve identifier memory 13 a. If an untried DCmask corresponding to the oscillation frequency does not exist (No atS28), an error message is displayed on the LCD 5 to indicate anoscillating status (S32), and the identifier of the DC mask curve is setto A. After the DC mask curve is set in S31 and S32, the connection withthe network is cut (S34), a flag stored in the DC mask curve settingcomplete flag memory of EEPROM 13 is set (S35), and the DC mask curvesetting process terminates.

As described above, with the communication apparatus 1 according to thesecond embodiment, the predetermined (default) DC mask curve andmultiple DC mask curves corresponding to respective oscillationfrequency bandwidths are defined. When the communication apparatus 1 isinstalled at the first time, the voltage-current characteristic isadjusted based on the predetermined DC mask curve. If an oscillation isgenerated in that condition, the DC mask curve corresponding to theoscillation frequency. Further, if an oscillation is still generated inthat condition, another DC mask curve corresponding to the oscillationfrequency is selected. Because the multiple DC mask curves are storedcorresponding to respective oscillation frequency bandwidths, even if anoscillation is generated when the voltage-current characteristic isadjusted based on the DC mask curve corresponding to the oscillationfrequency, another DC mask curve can be selected. Therefore, theoscillation in the network can be prevented more surely.

Next, a third embodiment will be described with reference to FIG. 8.Here, description similar to the first embodiment is omitted forbrevity, and discussion is made only on the different portions. In thefirst and second embodiments, the voltage-current characteristic isadjusted based on the predetermined (default) DC mask curve. If theoscillation is generated, another DC mask curve corresponding to theoscillation frequency is used for adjustment to cancel the oscillation.According to the third embodiment, the voltage-current characteristic isfirstly adjusted based on the predetermined (default) DC mask curve, andif an oscillation is generated in the network after the adjustment iscompleted, an untried DC curve is selected sequentially from the storedones in the memory.

In the third embodiment, the DC mask curves stored in ROM 12 are thesame as those of the first embodiment (see FIG. 4), and DC mask curveshaving the identifiers A, B, C and D are stored in this order.

FIG. 8 is a flowchart showing the DC mask curve setting processaccording to the third embodiment. The process is executed when thecommunication apparatus 1 is powered on.

First, the line voltage value detected by the voltage detection circuit34 is checked (S41). Then, it is judged whether the line voltage valueis equal to or greater than the minimum voltage which allows thecommunication apparatus 1 to connect with the communication line network(S42). If the line voltage is equal to or greater than the minimumvoltage (Yes at S42), the DC mask curve setting complete flag memory 13b of EEPROM 13 is checked, and it is judged whether the DC mask curvehas already been set (S43). If the DC mask curve has not been set (No atS43), the identifier A is stored in the Temp memory 14 a (S44), and theconnection with the network is cut (S45). Next, the voltage-currentcharacteristic adjustment process (see FIG. 11) is executed (S46). Inthe voltage-current characteristic adjustment process, the line voltageand the line current are adjusted based on the DC mask curve identifiedas A that is stored in ROM 12.

Next, after the adjustment is done in the voltage-current characteristicprocess, it is judged whether the oscillation is generated in thecommunication line network based on an oscillation detection signaloutput by the oscillation detection circuit 50 (S47). If the oscillationis generated in the communication line network (Yes at S47), it isjudged whether an untried DC mask curve exists among the curves storedin ROM 12 (S48). If an untried DC mask curve exists, the identifier ofthe DC mask curve is stored in the Temp memory 14 a (S49), and theprocess returns to the voltage-current characteristic adjustmentprocess.

If it is determined that the oscillation is not generated in the network(No at S47), the tried DC mask curve currently store the Temp memory 14a is set to be applied to the communication apparatus 1, while itsidentifier is stored in the DC mask curve identifier memory of EEPROM13. If an untried DC mask curve does not exist, an error message isdisplayed on LCD 5 indicating that an oscillation is generated using anyDC mask curve stored in ROM 12 (S51), and the identifier of the DC maskcurve is set to A (S52).

After the DC mask curve is set in S50 and S52, the connection with thenetwork is cut (S53), a flag stored in the DC mask curve settingcomplete flag memory 13 b of EEPROM 13 is set (S54), and the DC maskcurve setting process terminates. If in the process S42, the linevoltage is less than the minimum voltage allowing to connect with thenetwork (No at S42), or in the process S43, a DC mask curve is alreadyset (Yes at S43), the DC mask curve setting process terminates.

In addition, according to the third embodiment, it is not necessary todetect the oscillation frequency when an oscillation is generated in thenetwork, so the oscillation detection circuit 50 can output anoscillation detection signal when an output level of a high-pass filteris above the predetermined value where the line voltage is input to thehigh-pass filter of which cut off frequency is, for an example, 20 kHz.

As described above, with the communication apparatus 1 according to thethird embodiment, the ROM 12 stores multiple DC mask curves. If anoscillation is generated in the network when the voltage-currentcharacteristic is adjusted based on one of them, untried DC mask curvesare selected sequentially until the oscillation is suppressed, the DCmask curve is set to be applied to the communication apparatus 1 so asto prevent an oscillation in the network.

Next, a fourth embodiment is discussed with reference to FIG. 9. Here,repetitive description will be omitted, and description will be madeonly on different portions. In the first, second and third embodiments,the voltage-current characteristic is adjusted based on thepredetermined (default) DC mask curve. Then, after the adjustment, theoscillation detection circuit 50 detects whether an oscillation isgenerated, and according to the output of the oscillation detectioncircuit 50, one of DC mask curves stored in ROM 12 is selected.According to the fourth embodiment, the communication apparatus 1 has aselection controller with which a user can select any of the multiple DCmask curve. Then the user can select and set the most adequate DC maskcurve. In the fourth embodiment, two DC mask curves identified as A andB of multiple curves shown in FIG. 4 are employed.

The operational proceeds as follows. First, the DC mask curve selectionmode is set with the cursor key 4 a of the operation panel 4, etc. TheLCD 5 displays a message indicating the DC mask curve currently set. Foran example, when the DC mask curve identifier A is set, the message is“Level 1”, and when the DC mask curve identifier B is set, the messageis “Level 2”.

Next, when DC mask curve change is directed with the cursor key 4 a, themessage displayed on LCD 5 is changed. When the confirmation key 4 b ispressed, the changed DC mask curve is set.

FIG. 9 shows a flowchart of the process that is invoked when the DC maskcurve selection mode is set with the cursor key 4 a operation. The LCD 5displays a message indicating a setting screen for adjusting soundquality together with a message indicating the identifier of the DC maskcurve currently stored in the DC mask curve identifier memory 13 a ofEEPROM 13 (S61). Namely, when identifier A is stored in the DC maskcurve identifier memory 13 a of EEPROM 13, the message is “Level 1”, andwhen identifier B is stored, the message is “Level 2”.

Next, it is judged whether the controller to direct a change of thecurrently set DC mask curve is operated (S62). When the cursor key 4 ato change DC mask curves is operated (Yes at S62), it is judged whetherthe identifier of the currently set DC mask curve is A by referring tothe DC mask curve identifier memory 13 a (S63).

If the stored identifier is A (Yes at S63), LCD 5 displays the message“Level 2” (S64) and the identifier B is stored in the Temp memory 14 aof RAM 14. If the stored identifier is not A (No at S63), the LCD 5displays the message “Level 1” (S66) and the identifier A is stored inthe Temp memory 14 a of RAM 14.

In S64 or S65, when the identifier is stored in the Temp memory 14 a,the voltage-current characteristic adjustment is executed based on theDC mask curve identified by the identifier stored in the Temp memory 14a (S68). The voltage-current characteristic adjustment is the processshown in the flowchart in FIG. 11. Next, it is judged whether theconfirmation key 4 b is operated (S69). If the confirmation key 4 b isoperated (Yes at S69), the identifier stored in the Temp memory 14 a isstored in the DC mask curve identifier memory 13 a of EEPROM 13 (S70).

As described above, according to the communication apparatus 1 of thefourth embodiment, two DC mask curves are stored in ROM 12, and a usercan select any of the two DC mask curves to be applied to adjustment ofthe voltage-current characteristic. Therefore, the voltage-currentcharacteristic is adjusted based on the selected DC mask curve. If anoscillation is generated in that condition, the other DC mask curve canbe selected.

In particular, when a telephone set is built in the communicationapparatus 1 and the connection with the network is established, the usercan select and set the DC mask curve so as to suppress noise caused bythe oscillation generated in the network checking with a handsetreceiver.

In the first embodiment of the communication apparatus 1, thecommunication apparatus is a multiple function processing machine whichhas multiple functions such as, facsimile, copier, scanner, telephone.However, the invention is not limited to this embodiment. Thecommunication apparatus 1 may a single function communication apparatus.In the first embodiment of the communication apparatus 1, thecommunication apparatus 1 has a voltage detection section which detectsthe line voltage, and the line current is calculated based on the lineimpedance. The communication apparatus 1 may have a current detectionsection instead of a voltage detection section, and the line voltage iscalculated based on the line impedance. The communication apparatus 1may also have both a voltage detection section and a current detectionsection. Further, in the first embodiment of the communication apparatus1, when an oscillation is generated in the network, the oscillationfrequency is acquired and the voltage-current characteristic is selectedcorresponding to the oscillation frequency. When an oscillation isgenerated in the network, a oscillation level may be detected, and thevoltage-current characteristic curve is selected corresponding to theoscillation level.

1 A communication apparatus, comprising: a line control unit configured to control connection with a communication line network; a communication unit configured to transmit and receive data through the communication line network; a detection circuit configured to detect one of a line voltage value and a line current value when the communication apparatus is connected to the line network; a memory unit configured to store multiple voltage-current characteristic curves defining relationships of line voltage values with respect to line current values; an adjusting unit configured to obtain the line voltage and the line current based on the one of the line voltage value and the line current value, and adjusting the line voltage value and the line current value based on one of the voltage-current characteristic curves stored in the memory unit; a selecting unit configured to select another voltage-current characteristic curve which is different from the one of the voltage-current characteristic curves from among the multiple voltage-current characteristic curves stored in the memory unit; and a re-adjusting unit configured to control the adjusting unit based on the selected voltage-current characteristic curve selected by the selecting unit.
 2. The communication apparatus according to claim 1, wherein the memory unit stores two voltage-current characteristic curves, and wherein the selecting unit is configured to switch the selected voltage-current characteristic curve to the other voltage-current characteristic curve when one of the line voltage and line current is adjusted by the adjusting unit.
 3. The communication apparatus according to claim 1, further comprising an oscillation detection circuit that detects whether an oscillation is generated in the communication line network, and wherein the selecting unit selects another voltage-current characteristic curve if the oscillation detection circuit detects that an oscillation is generated at the line voltage and the line current adjusted by the adjusting unit.
 4. The communication apparatus according to claim 3, wherein the memory unit stores more than two voltage-current characteristic curves, and wherein the selecting unit sequentially selects one of the voltage-current characteristic curve among more than two voltage-current characteristic curves store in the memory unit if the oscillation detection circuit detects the oscillation in the communication line network after the line voltage and the line current are adjusted by the adjusting unit.
 5. The communication apparatus according to claim 1, further comprising an oscillation detection circuit that detects whether an oscillation is generated in the communication line network, the oscillation detection circuit obtaining an oscillation frequency if the oscillation is detected, wherein the memory unit stores a voltage-current characteristic curve corresponding to the oscillation frequency if an oscillation is detected in the communication line network, and wherein the selecting unit selects the voltage-current characteristic curve corresponding to the oscillation frequency detected by the oscillation detection circuit from the ones stored in the memory unit.
 6. The communication apparatus according to claim 5, wherein the memory unit is configured to store multiple voltage-current characteristic curves corresponding to an oscillation frequency of an oscillation generated in the communication line network, and wherein another voltage-current characteristic curve corresponding to the oscillation frequency detected by the oscillation detection circuit is selected if the oscillation detection circuit detects that an oscillation is generated in the communication line network at the line voltage value and the line current value previously adjusted by the adjusting unit.
 7. The communication apparatus according to claim 3, wherein, if the oscillation detection circuit detects an oscillation in the communication line network at the line voltage value and the line current value adjusted with the adjusting unit, the selecting unit selects a different one of the multiple voltage-current characteristic curves.
 8. The communication apparatus according to claim 7, wherein the selecting unit includes a selected voltage-current characteristic curve memory unit that stores the selected voltage-current characteristic curve , and wherein the selecting unit selects a voltage-current characteristic curve which is not store in the tried voltage-current characteristic curve memory.
 9. The communication apparatus according to claim 1, wherein the communication apparatus includes an operable member that allows a user to manually select one of the multiple voltage-current characteristic curves stored in the memory unit.
 10. The communication apparatus according to claim 9, wherein the operable member allows a user to select one of the multiple voltage-current characteristic curves when a connection with the communication line network is established.
 11. A method of adjusting one of a line voltage and a line current applied to a communication line of a communication apparatus, the communication line being connected to a communication line network, the method comprising: storing multiple voltage-current characteristic curves; adjusting one of the line voltage and the line current based one on of the multiple voltage-current characteristic curves; detecting whether an oscillation is generated in a communication line network, a line control unit configured to control connection with a communication line network; transmitting and receiving data through the communication line network; and re-adjusting one of the line voltage and the line current based on another one of the multiple voltage-current characteristic curves.
 12. A computer program product comprising computer readable instructions that cause a computer to execute a method of adjusting one of a line voltage and a line current applied to a communication line of a communication apparatus, the communication line being connected to a communication line network, the method comprising: storing multiple voltage-current characteristic curves; adjusting one of the line voltage and the line current based on one of the multiple voltage-current characteristic curves; detecting whether an oscillation is generated in a communication line network, a line control unit configured to control connection with the communication line network; a communication unit configured to transmit and receive data through the communication line network; and re-adjusting one of the line voltage and the line current based on another one of the multiple voltage-current characteristic curves. 